Liquefied natural gas (LNG) and other very low temperature fluids are of increasing, commercial importance. There is, therefore, a need for increased facility in handling, storing, and transporting such liquids. For example, LNG is being increasingly utilized as an alternative fuel source for internal combustion engines. Governmental regulations require that LNG be transported at pressures of about 30 psi, but to decrease the amount of LNG that is evaporated or otherwise lost from a stationary storage tank, it is common to store the LNG at pressures of 150 psi. When "bottled" for use as the fuel for an internal combustion engine, it is common to pressurize the LNG to pressures as high as 220 psi. Of course each increase in pressure requires that the LNG be pumped into either a storage tank or into a fuel tank at the next higher pressure such that successful use of LNG as an alternative fuel depends, in effect, upon reliable, safe and energy efficient pumping of high volumes of such fluids at very low temperatures.
Pumps presently used for pumping low temperature fluids all suffer from a variety of disadvantages and limitations which limit their life, require frequent maintenance, and otherwise decrease their utility. This is particularly true when the temperature of the fluid must be very low. For instance, pumps that are currently available for pumping LNG, but wear out quickly and need frequent maintenance and particularly require frequent replacement of the seals. Heretofore known seal-less pumps have not provided a satisfactory solution to this problems. For instance, magnetic drive pumps known in the fluid pump art, are not reliable for use at very low temperatures. Bonding material utilized on the magnets at low temperature nevertheless fails at very low temperature. In the case of LNG, severe problems result from the almost complete lack of lubrication that is provided by the LNG passing through the pump.
It is, therefore, an object of the present invention to provide a pump for use at very low temperatures which is not limited by the disadvantages of known pumps. More specifically, it is a n object of the present invention to provide a seal-less magnetic drive pump for use in pumping at very low temperatures.
Another object of the present invention is to provide a magnetic drive pump useful at very low temperatures used herein to mean temperatures lower than about -100.degree. C. Yet another object of the present invention is to provide a magnetic drive pump which is self lubricated when used for pumping, for instance, such high volume, commonly utilized fluids as LNG and liquid nitrogen.